Problem: Gaps in Speech

This may be due to a high rate of packet loss
or packet discard due to jitter, or to a problem,
with Voice Activity Detection associated with an echo canceller.

The Voice over IP hardware may be configured to use silence insertion
instead of packet loss concealment, hence during
a period of high loss or congestion many short segments of speech can
be missing.

Voice Activity Detection is used with some CODECs to determine if speech
energy is present. If there is no speech energy present then packets
are not transmitted. Echo cancellers use a similar voice energy detection
algorithm to mask echo in low level speech signals (echo suppression)
and may insert silence.

Resolution

Investigate the source of packet loss or
packet discard problems and verify that the
jitter buffer is set to a sufficient depth. Verify that the VoIP hardware
is configured to use packet loss concealment.
Check for excessive route changes or link failures in core IP network.

If there is no apparent packet loss or discard then check the operation
of Gateway echo cancellers.

Tools:

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